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Aspects and Applications of Non-Axisymmetric Coils on KSTAR
Y.M. Jeon
On behalf of S.W. Yoon, J.H. Kim, S.H. Hahn, W.C. Kim, Y.K. Oh, Jong-Gu Kwak, W.H. Ko, S.G. Lee, J.G. Bak, K.D. Lee, Y.U. Nam, J.Y. Kim, H.L. Yang, H.K. Kim and KSTAR team
National Fusion Research Institute (NFRI), Korea
in collaborations with Princeton Plasma Physics Laboratory, USA (J.-K. Park)
General Atomics, USA (D.A. Humphreys, M. Walker, A. Welander) Columbia University, USA (S.A. Sabbagh, Y.S. Park)
2011.11.21 General Atomics, San Diego, USA
16th Workshop on MHD Stability Control
1. Overview of 3D Field Coils in KSTAR
2. Applications
2-1. Axisymmetric Applications
2-2. 3D (Non-axisymmetric) Applications
- ELM suppression by n=1 RMP
3. Summary
2011-11-21 2 16th Workshop on MHD Stability Control - Y.M. Jeon
1. Overview of 3D Field Coils in KSTAR
2. Applications
2-1. Axisymmetric Applications
2-2. 3D (Non-axisymmetric) Applications
- ELM suppression by n=1 RMP
3. Summary
2011-11-21 3 16th Workshop on MHD Stability Control - Y.M. Jeon
KSTAR Has A Versatile In-Vessel Control Coil (IVCC)
System Inside Vacuum Vessel
2011-11-21 4 16th Workshop on MHD Stability Control - Y.M. Jeon
•Toroidally segmented 3D shaped coil system (1) Combining axisymmetric and non-axisymmetric field coils
(2) Easier installation and maintenance
Top IVCC Upper IVCC
Lower IVCC Bottom IVCC
Circular Part
Straight Part
* H.K. Kim, H.L. Yang, et al., Fus. Eng. Design 84 (2009)
Applicable to Axisymmetric and Non-Axisymmetric
Magnetic Applications
2011-11-21 5 16th Workshop on MHD Stability Control - Y.M. Jeon
Schematic Diagram
Upper IVC
Top FEC
Upper IRC
Middle FEC
Lower IVC
Bottom FEC
Lower IRC
Upper Vertical
Control Coil
Upper Radial
Control Coil
Top FEC
Middle FEC
Bottom FEC
Lower Radial
Control Coil
Lower Vertical
Control Coil
Bottom IVCC Lower IVCC
Top IVCC Upper IVCC
•Axisymmetric applications -Vertical stability control (IVC), fast radial control (IRC)
•Non-axisymmetric (3D) applications -Field error corrections (FEC), RWM, RMP etc
Top-FEC
Mid-FEC
Bot-FEC
Bottom IVCC
Lower IVCC
Top IVCC
Upper IVCC
Full IVCC System Installed in 2010
2011-11-21 6 16th Workshop on MHD Stability Control - Y.M. Jeon
IVCC
Passive
Stabilizer
Full IVCC System Installed in 2010
2011-11-21 7 16th Workshop on MHD Stability Control - Y.M. Jeon
1. Overview of 3D Field Coils in KSTAR
2. Applications
2-1. Axisymmetric Applications
2-2. 3D (Non-axisymmetric) Applications
- ELM suppression by n=1 RMP
3. Summary
2011-11-21 8 16th Workshop on MHD Stability Control - Y.M. Jeon
Successful Vertical Stabilizations of Highly Shaped
Plasmas by IVC (~1.85 and ~1.0)
2011-11-21 9 16th Workshop on MHD Stability Control - Y.M. Jeon
• ~1.85 & ~1.0 achieved successfully
• Led to early achievement of first H-mode (2010)
Zcur Zgeo
Upper IVC
Lower IVC
Even LSN Plasmas Enforced by IVC Were Well
Controlled
2011-11-21 10 16th Workshop on MHD Stability Control - Y.M. Jeon
Zcur
Zgeo
• For LSN shaping, plasma pushed down by ~10cm using IVC - IIVC~2.0kA/t applied to hold it
• Well controlled even though its worse field curvature
Integrated Shape Control Combined with IRC Can
Enhance Control Performance Significantly
2011-11-21 11 16th Workshop on MHD Stability Control - Y.M. Jeon
• IRC is not essential component, but …
• Can enhance shape control performance
significantly
• Improved shape control=
“Fast Rp control by IRC”
+ “isoflux control with Mij-decoupling”
• Example: All volume shifted by R=+2cm
IRC is on preparation for use in 2012
Upper IRC
Lower IRC
1. Overview of 3D Field Coils in KSTAR
2. Applications
2-1. Axisymmetric Applications
2-2. 3D (Non-axisymmetric) Applications
- ELM suppression by n=1 RMP
3. Summary
2011-11-21 12 16th Workshop on MHD Stability Control - Y.M. Jeon
n=2
n=1
-BR
+BR
KSTAR Can Provide Wide Spectra of 3D Magnetic
Perturbations
Top-FEC
Mid-FEC
Bot-FEC
• 3-by-4 3D field coils available having 2 turns for each
- all internal and segmented with saddle loop configurations
- n=1 and 2 applicable
• Wide spectra of magnetic perturbations are possible
- Poloidal helicity change for n=1
- Even/odd parity change for n=2
2011-11-21 13 16th Workshop on MHD Stability Control - Y.M. Jeon
Main applications of 3D fields 1. Resistive Wall Mode Control
2. Error Field Correction
3. RMP/NRMP Physics Study
Top-FEC
Mid-FEC
Bot-FEC
+ + - -
- - + +
- + + -
n=1, +90 phase
RWM Controls Are Under Design and Study
: Cu-Passive Stabilizer + RWM coils N,Wall(~5.0)
2011-11-21 14 16th Workshop on MHD Stability Control - Y.M. Jeon
In VALEN model
* Y.S. Park, S.A. Sabbagh, et al., Nucl. Fusion 51 (2011)
MISK predicts
relatively large
rotations are required
for RWM stability
Controlled
within ~8ms
Middle FEC
Applicable Spectra of n=1 and n=2 MP
top
mid
bot
- - + +
+ + - -
- + + -
n=1, -90 phase
top
mid
bot
+ + - -
+ + - -
- - + +
n=1, 180 phase
top
mid
bot
+ + - -
+ + - -
+ + - -
n=1, 0 phase
top
mid
bot
+ + - -
n=1, mid-FEC alone
top
mid
bot
+ - + -
- + - +
n=2, odd parity
2011-11-21 15 16th Workshop on MHD Stability Control - Y.M. Jeon
top
mid
bot
+ + - -
- - + +
- + + -
n=1, +90 phase
BT
top
mid
bot
+ - + -
+ - + -
- + - +
n=2, even parity
+
Non-Axisymmetric Plasma Responses Were Investigated
Using Two Different Phasings
2011-11-21 16 16th Workshop on MHD Stability Control - Y.M. Jeon
• Two different phasings (+90 and -90) of the n=1 fields were applied to
Ohmic discharges (IP=400kA, BT=2.0T)
– The +90 phasing induced a locking and disruption with IFEC~600A/turn
– The -90 phasing caused only a slight braking of rotation
Magnetic braking
5934 +90 phasing
5933 -90 phasing
Locking
- - + +
+ + - -
- + + -
-90 (Non-resonant)
+ + - -
- - + +
- + + -
+90 (Resonant)
B-field
* J.-K. Park, Y.M. Jeon, et al., in preparation for publication
6015 : 0 phase
6016 : 180 phase
Locking
Non-Axisymmetric Plasma Responses Were Found In +90
Phasing By Locking
2011-11-21 17 16th Workshop on MHD Stability Control - Y.M. Jeon
• A small non-axisymmetry was found in +90 phasing, by applying two
different toroidal phases
– Locking threshold IFEC~1kA/turn for 0 phase, IFEC~1.2kA/turn for 180 phase
A small intrinsic error-field (~100A) found in KSTAR
Error field
~100A
Locking Threshold
Locking level
(m,n)=(2,1) 0 180 Mid
90 90
[by IPEC]
1. Overview of 3D Field Coils in KSTAR
2. Applications
2-1. Axisymmetric Applications
2-2. 3D (Non-axisymmetric) Applications
- ELM suppression by n=1 RMP
3. Summary
2011-11-21 18 16th Workshop on MHD Stability Control - Y.M. Jeon
ELMs Suppressed by n=1 MPs in KSTAR 2011
2011-11-21 19 16th Workshop on MHD Stability Control - Y.M. Jeon
• COMPASS-D (n=1) triggered (2001)
• DIII-D (n=3) suppressed (2004)
• JET (n=1, 2) mitigated (2007)
• NSTX (n=3) triggered (2010)
• MAST (n=3) mitigated (2011)
• ASDEX-U (n=2) mitigated (2011)
We are adding … • KSTAR (n=1) Suppressed (2011) * Y.M. Jeon, J.-K. Park, et al., submitted to PRL (Nov 05, 2011)
ELMs Suppressed For the First Time by n=1 MP (+90)
2011-11-21 20 16th Workshop on MHD Stability Control - Y.M. Jeon
• +90 phased n=1 MP suppressed ELMs - In JET, ELM mitigated by n=1 (Y.Liang, PRL,
2007)
• Density (~10%) pumping out initially.
Then, increased when ELM suppressed
• Stored energy drop by ~8% initially.
Then slightly increased or sustained
when ELM suppressed
• Rotation decreased (~10%) initially.
Then sustained when ELM suppressed
• Te/Ti changes were relatively small
• Two distinctive phases observed
(1)ELM excitation phase
(2)ELM suppression phase
Threshold FEC Current for ELM Suppression
2011-11-21 21 16th Workshop on MHD Stability Control - Y.M. Jeon
Fully
suppressed
Fully
suppressed
Marginally
suppressed
Marginally
suppressed
No effect or
Weakly mitigated
• IFEC,threshold 0.75 kA/t : marginal suppression
> 1.00 kA/t : full suppression (vacuum analysis predicted 1.00 kA/t)
• p is dependent on IFEC
(similar ne, Wtot, V, …)
• Note that there was no clear change of ELM size on transition
(excitation suppression), while the ELM frequency decreased dramatically
ELMs Suppressed For the First Time by n=1 MP (+90)
2011-11-21 22 16th Workshop on MHD Stability Control - Y.M. Jeon
• +90 phased n=1 MP suppressed ELMs - In JET, ELM mitigated by n=1 (Y.Liang, PRL,
2007)
• Density (~10%) pumping out initially.
Then, increased when ELM suppressed
• Stored energy drop by ~8% initially.
Then slightly increased or sustained
when ELM suppressed
• Rotation decreased (~10%) initially.
Then sustained when ELM suppressed
• Te/Ti changes were relatively small
• Two distinctive phases observed
(1)ELM excitation phase
(2)ELM suppression phase
Mid-FEC May Responsible for ELM-Excitation
2011-11-21 23 16th Workshop on MHD Stability Control - Y.M. Jeon
• ELMs excitation observed as
expected
• Similar evolutions of global
parameters with those on the
initial ELM-excited phase
• Note that ELM-excitation should
be distinguished from ELM-
triggering
• Therefore, mixed MPs made two
phases ELMs
i.e. ‘mid-FEC alone’ + ‘n=1, +90’
ELMs Were Suppressed Rather Than Mitigated
2011-11-21 24 16th Workshop on MHD Stability Control - Y.M. Jeon R[cm]
Z [
cm]
#6123 IFEC=1.9kA/t
A B C
* G.S. Yun, APS invited, YI2 (2011)
Unusual Pedestal Evolutions Observed Suggesting Edge
Transport Change by MP
• Observations are … - Pedestal buildup saturated in the
intermediate level - When destabilized, it resume pedestal
build-up until the original threshold level.
- After crash, it became back to the original crashed level
- Edge stability seems to be not much changed
ELM excited
KSTAR #5947
(MP-on phase)
ELM suppressed
2011-11-21 25 16th Workshop on MHD Stability Control - Y.M. Jeon
Experimental Evidence for Edge Transport Change by
MPs Saturation of Pedestal Evolution
2011-11-21 26 16th Workshop on MHD Stability Control - Y.M. Jeon
#5947
ELM-suppressed
ELM Crash Saturated build-up
Of pedestal
1.0
* RMP fully applied
in this time period
1.0
Gradual build-up
Of pedestal
Crash
Specific Changes of Magnetic Fluctuation May Be A Clue
Or Evidence for Edge Transport Change
2011-11-21 27 16th Workshop on MHD Stability Control - Y.M. Jeon
Without MP
ELM-suppressed -Fluctuation rising -Mid-plane dominant -Broad (not specific) spectrum
ELM-excited -Fluctuation reduced -both midplane and divertor
Vacuum Analysis for n=1 Magnetic Perturbations
0 +90
180 -90
mid-alone
* CH=stochastic layer width in the edge
Resonant MP (RMP)
Non-Resonant (NRMP)
2011-11-21 28 16th Workshop on MHD Stability Control - Y.M. Jeon
IPEC With Plasma Responses Predicts Somewhat
Differently
2011-11-21 29 16th Workshop on MHD Stability Control - Y.M. Jeon
Vacuum IPEC 0 +90
180 -90
mid-alone
0 +90
180 -90
mid-alone
IPEC+NTV 0
+90
180
-90
mid
•180 phase is the best for Chirikov
•180 phase may have strongest rotation
damping
Experimental Observations for Wide MP Spectra
2011-11-21 30 16th Workshop on MHD Stability Control - Y.M. Jeon
ELM Suppression
ELM Excitation
H/L Back-transition / Locking
ELM (strong) mitigation ~ JET n=1
ELM Excitation
H/L back-transition
(a)
(b)
(c)
(d)
(e)
Div
ert
or
D
[a
.u.]
• Variety of ELM responses to different MP spectra • Various ELM controllability of MPs
Occasionally, HL Transition and Locking Observed
Instead of ELM-Suppression, Responding to n=1 MPs
L H
RMP-On
ELM suppressed
LH & Locking
• Mode locking was one of expected
plasma responses to n=1 MP
• A key difference in HL/Locked
discharges compared with ELM-
suppressed ones is the larger
increase of edge Te in H-mode by a
factor of ~2.
May correlated with edge
collisionality
2011-11-21 31 16th Workshop on MHD Stability Control - Y.M. Jeon
Strong Magnetic Braking by n=1 MP Observed
: Complete Locking Without Killing Plasmas
2011-11-21 32 16th Workshop on MHD Stability Control - Y.M. Jeon
0.0
0.5
1.0
1.5
2.0
Ti [k
eV
]
#6258 @ 4.265
#6258 @ 4.285
#6258 @ 4.295
#6258 @ 4.305
#6258 @ 4.315
#6258 @ 4.325
#6258 @ 4.335
1.8 1.9 2.0 2.1 2.2 2.3-20
0
20
40
60
80
Vt
[km
/sec]
Major radius [m]
#6258 @ 4.265
#6258 @ 4.285
#6258 @ 4.295
#6258 @ 4.305
#6258 @ 4.315
#6258 @ 4.325
#6258 @ 4.335
#6258
CES profile
PECH
2/1 tearing
ELMs Triggered by n=2 With Odd Parity
2011-11-21 33 16th Workshop on MHD Stability Control - Y.M. Jeon
• Two ELM-free H-mode periods
• n=2 with odd-parity triggered type-I ELMs
• Vtor didn’t changed by L/H transition
strong mag. braking
• Ref to ELM triggering on NSTX by n=3 MP
#6369
n=2, odd-parity
Mag. braking
Divertor
Mid-plane
Summary And Discussion
2011-11-21 34 16th Workshop on MHD Stability Control - Y.M. Jeon
1. Versatile IVCC system in KSTAR - Axisymmetric + non-axisymmetric (n=1, 2) - Three poloidal coils wide spectra of MPs - Various applications: IVC, IRC + FEC, RWM, RMP
2. ELM control by applying non-axisymmetric MPs - ELMs suppressed completely by n=1 MP - Various ELM responses : suppression, excitation, mitigation, locking, triggering - Saturated pedestal evolutions with specific change of mag. fluctuations - Strong mag. braking by n=1 MPs
3. Worth to note that … - Variety of ELM responses to different mag. spectra - Wide controllability of ELMs by applying MPs - Important to understand what made different responses such as
mitigation excitation suppression triggering